<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* div {
            width: 10vw;
            height: 10vw;
            background: tomato
        } */
        .f {
            width: 50px;
            height: 50px;
        }
        .s {
            width: 20%;
            height: 0;
            padding-top: 20%;
            background: turquoise;
        }
    </style>
</head>
<body>
    <div class="f">
        <div class="s"></div>
    </div>
</body>
</html>